This invention relates to a new and useful catalyst for oxidizing hydrogen, as is for example desired at the hydrogen electrode of a hydrogen-oxygen low-temperature fuel cell, and as is desirable in many other chemical reactions involving hydrogenation.
There are many such reactions in which hydrogenation is important, and many catalysts have been proposed and used for such purposes. In certain applications such as the fuel cell application mentioned above, in which the H.sub.2 molecule is supplied to an electrode of the fuel cell, the catalyst aids in the splitting apart of the H.sub.2 molecule into H.sup.+ atoms in the electrolyte adjacent the electrode, whereby an electron is transferred to the electrode as desired in the generation of useful fuel cell current; the H.sup.+ hydrogen atoms combine with O.sup.-.sup.- oxygen atoms produced at the other fuel cell electrode to form water in the electrolyte. In this process the hydrogen is oxidized in the sense that it acquires a more positive charge i.e. a higher valence. Without a suitable catalyst present, the hydrogen and oxygen will not act as desired to any substantial extent, and there will be no useful fuel cell current.
There are a variety of other applications in which a catalyst is desired to provide oxidizing of hydrogen to facilitate a chemical reaction, for example in the reaction of organic compounds such as are involved in the conversion of shale to useful petroleum products, or in the conversion of noxious engine exhausts to less harmful products by means of catalytic converters.
New catalysts are desired not only from the broad viewpoint that any new catalyst widens the range of raw materials from which catalysts can be made, but also from the viewpoint of obtaining an improved combination of cost and performance of the catalyst. For example, platinum by itself is an excellent catalyst for many purposes, but its cost becomes prohibitive in many applications. It is therefore desirable to provide catalysts of materials which are of less cost per unit mass, or to increase the activity of platinum so that its high cost is more nearly compensated by better performance.
Various mixtures or alloys of different elements have been proposed for use as catalysts, and some have exhibited usefully high catalytic activity at least initially. However, one difficulty which has been encountered in at least some of such catalysts is that when the two or more closely-adjacent components of the mixture or alloy are simultaneously exposed to the electrolyte or other component in the desired chemical reaction, the components of the catalyst often form an electrochemical couple, resulting in dissolution or "leaching" of one component of the catalyst, thereby impairing the useful life of the catalyst.
Accordingly, it is an object of the invention to provide a new and useful hydrogen-oxidizing catalyst, and a fuel cell electrode using same.
Another object is to provide such catalyst which provides excellent activity, especially in view of the cost thereof.
Another object is to provide such catalyst which is substantially impervious to the type of leaching or dissolving action which tends to occur in many types of catalysts involving more than one component, due to interactions with the adjacent chemical environment such as an electrolyte in contact with each of the different components of the catalyst.
It is also an object to provide a fuel cell electrode using the catalyst of the invention, especially a hydrogen electrode for a low-temperature hydrogen-oxygen fuel cell.